I just got my first betta, blue, a few days ago. He is very happy blowing bubbles and swimming alot. But I keep my dorm room at 74*, and I have a lamp next to his tank, do you guys think that I need to get a heater for his tank or should he be fine?

I have a 1 1/2 gallon bowl for him, and he seems pretty happy! He's currently working on a bubble nest!
Oh and I will be gone from Friday until Monday coming up and I was wondering what I should do with the fish? Should I leave his lamp on, should I leave extra food in his tank? I appreciate any help...

He won't starve over the weekend. There are many people that will skip a day or 2 of feeding every week to make sure they don't accidentally overfeed. I would not want to leave the light on continuously for days at a time. Bettas need a light and dark cycle just like people do.

Leave him near a window so that he gets day and night, but don't put him on the windowsill or anything like that. Direct sunlight often leads to an algae outbreak.

I would also recommend a heater. your temperature isn't as bad as many I have seen on this forum, but when night comes it will drop, and often the drop is very stressful on the fish whereas a heater will keep it nice and steady.